gcc/tree-ssanames.c

   1 /* Generic routines for manipulating SSA_NAME expressions
   2    Copyright (C) 2003 Free Software Foundation, Inc.
   3
   4 This file is part of GCC.
   5
   6 GCC is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2, or (at your option)
   9 any later version.
  10
  11 GCC is distributed in the hope that it will be useful,
  12 but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 GNU General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GCC; see the file COPYING.  If not, write to
  18 the Free Software Foundation, 59 Temple Place - Suite 330,
  19 Boston, MA 02111-1307, USA.  */
  20
  21 #include "config.h"
  22 #include "system.h"
  23 #include "coretypes.h"
  24 #include "tm.h"
  25 #include "tree.h"
  26 #include "varray.h"
  27 #include "ggc.h"
  28 #include "tree-flow.h"
  29
  30 /* Rewriting a function into SSA form can create a huge number of SSA_NAMEs,
  31    many of which may be thrown away shortly after their creation if jumps
  32    were threaded through PHI nodes.
  33
  34    While our garbage collection mechanisms will handle this situation, it
  35    is extremely wasteful to create nodes and throw them away, especially
  36    when the nodes can be reused.
  37
  38    For PR 8361, we can significantly reduce the number of nodes allocated
  39    and thus the total amount of memory allocated by managing SSA_NAMEs a
  40    little.  This additionally helps reduce the amount of work done by the
  41    garbage collector.  Similar results have been seen on a wider variety
  42    of tests (such as the compiler itself).
  43
  44    Right now we maintain our free list on a per-function basis.  It may
  45    or may not make sense to maintain the free list for the duration of
  46    a compilation unit.
  47
  48    External code should rely solely upon HIGHEST_SSA_VERSION and the
  49    externally defined functions.  External code should not know about
  50    the details of the free list management.
  51
  52    External code should also not assume the version number on nodes is
  53    monotonically increasing.  We reuse the version number when we
  54    reuse an SSA_NAME expression.  This helps keep arrays and bitmaps
  55    more compact.
  56
  57    We could also use a zone allocator for these objects since they have
  58    a very well defined lifetime.  If someone wants to experiment with that
  59    this is the place to try it.  */
  60
  61 /* Array of all SSA_NAMEs used in the function.  */
  62 varray_type ssa_names;
  63
  64 /* Bitmap of ssa names marked for rewriting.  */
  65 bitmap ssa_names_to_rewrite;
  66
  67 /* Free list of SSA_NAMEs.  This list is wiped at the end of each function
  68    after we leave SSA form.  */
  69 static GTY (()) tree free_ssanames;
  70
  71 /* Version numbers with special meanings.  We start allocating new version
  72    numbers after the special ones.  */
  73 #define UNUSED_NAME_VERSION 0
  74
  75 #ifdef GATHER_STATISTICS
  76 unsigned int ssa_name_nodes_reused;
  77 unsigned int ssa_name_nodes_created;
  78 #endif
  79
  80 /* Returns true if ssa name VAR is marked for rewrite.  */
  81
  82 bool
  83 marked_for_rewrite_p (tree var)
  84 {
  85   if (ssa_names_to_rewrite
  86       && bitmap_bit_p (ssa_names_to_rewrite, SSA_NAME_VERSION (var)))
  87     return true;
  88
  89   return false;
  90 }
  91
  92 /* Returns true if any ssa name is marked for rewrite.  */
  93
  94 bool
  95 any_marked_for_rewrite_p (void)
  96 {
  97   if (!ssa_names_to_rewrite)
  98     return false;
  99
 100   return bitmap_first_set_bit (ssa_names_to_rewrite) != -1;
 101 }
 102
 103 /* Mark ssa name VAR for rewriting.  */
 104
 105 void
 106 mark_for_rewrite (tree var)
 107 {
 108   if (!ssa_names_to_rewrite)
 109     ssa_names_to_rewrite = BITMAP_XMALLOC ();
 110
 111   bitmap_set_bit (ssa_names_to_rewrite, SSA_NAME_VERSION (var));
 112 }
 113
 114 /* Unmark all ssa names marked for rewrite.  */
 115
 116 void
 117 unmark_all_for_rewrite (void)
 118 {
 119   if (!ssa_names_to_rewrite)
 120     return;
 121
 122   bitmap_clear (ssa_names_to_rewrite);
 123 }
 124
 125 /* Return the bitmap of ssa names to rewrite.  Copy the bitmap,
 126    so that the optimizers cannot access internals directly  */
 127
 128 bitmap
 129 marked_ssa_names (void)
 130 {
 131   bitmap ret = BITMAP_XMALLOC ();
 132   if (ssa_names_to_rewrite)
 133     bitmap_copy (ret, ssa_names_to_rewrite);
 134
 135   return ret;
 136 }
 137
 138 /* Initialize management of SSA_NAMEs.  */
 139
 140 void
 141 init_ssanames (void)
 142 {
 143   VARRAY_TREE_INIT (ssa_names, 50, "ssa_names table");
 144
 145   /* Version 0 is special, so reserve the first slot in the table.  Though
 146      currently unused, we may use version 0 in alias analysis as part of
 147      the heuristics used to group aliases when the alias sets are too
 148      large.  */
 149   VARRAY_PUSH_TREE (ssa_names, NULL_TREE);
 150   free_ssanames = NULL;
 151 }
 152
 153 /* Finalize management of SSA_NAMEs.  */
 154
 155 void
 156 fini_ssanames (void)
 157 {
 158   free_ssanames = NULL;
 159 }
 160
 161 /* Dump some simple statistics regarding the re-use of SSA_NAME nodes.  */
 162
 163 #ifdef GATHER_STATISTICS
 164 void
 165 ssanames_print_statistics (void)
 166 {
 167   fprintf (stderr, "SSA_NAME nodes allocated: %u\n", ssa_name_nodes_created);
 168   fprintf (stderr, "SSA_NAME nodes reused: %u\n", ssa_name_nodes_reused);
 169 }
 170 #endif
 171
 172 /* Return an SSA_NAME node for variable VAR defined in statement STMT.
 173    STMT may be an empty statement for artificial references (e.g., default
 174    definitions created when a variable is used without a preceding
 175    definition).  */
 176
 177 tree
 178 make_ssa_name (tree var, tree stmt)
 179 {
 180   tree t;
 181
 182 #if defined ENABLE_CHECKING
 183   if ((!DECL_P (var)
 184        && TREE_CODE (var) != INDIRECT_REF)
 185       || (stmt
 186           && !IS_EXPR_CODE_CLASS (TREE_CODE_CLASS (TREE_CODE (stmt)))
 187           && TREE_CODE (stmt) != PHI_NODE))
 188     abort ();
 189 #endif
 190
 191   /* If our free list has an element, then use it.  Also reuse the
 192      SSA version number of the element on the free list which helps
 193      keep sbitmaps and arrays sized HIGHEST_SSA_VERSION smaller.  */
 194   if (free_ssanames)
 195     {
 196       unsigned int save_version;
 197
 198       t = free_ssanames;
 199       free_ssanames = TREE_CHAIN (free_ssanames);
 200 #ifdef GATHER_STATISTICS
 201       ssa_name_nodes_reused++;
 202 #endif
 203
 204       /* Clear the node so that it looks just like one we would have
 205          received from make_node.  */
 206       save_version = SSA_NAME_VERSION (t);
 207       memset (t, 0, tree_size (t));
 208       TREE_SET_CODE (t, SSA_NAME);
 209       SSA_NAME_VERSION (t) = save_version;
 210     }
 211   else
 212     {
 213       t = make_node (SSA_NAME);
 214       SSA_NAME_VERSION (t) = num_ssa_names;
 215       VARRAY_PUSH_TREE (ssa_names, t);
 216 #ifdef GATHER_STATISTICS
 217       ssa_name_nodes_created++;
 218 #endif
 219     }
 220
 221   TREE_TYPE (t) = TREE_TYPE (var);
 222   SSA_NAME_VAR (t) = var;
 223   SSA_NAME_DEF_STMT (t) = stmt;
 224   SSA_NAME_PTR_INFO (t) = NULL;
 225   SSA_NAME_IN_FREE_LIST (t) = 0;
 226
 227   return t;
 228 }
 229
 230
 231 /* We no longer need the SSA_NAME expression VAR, release it so that
 232    it may be reused.
 233
 234    Note it is assumed that no calls to make_ssa_name will be made
 235    until all uses of the ssa name are released and that the only
 236    use of the SSA_NAME expression is to check its SSA_NAME_VAR.  All
 237    other fields must be assumed clobbered.  */
 238
 239 void
 240 release_ssa_name (tree var)
 241 {
 242   /* Never release the default definition for a symbol.  It's a
 243      special SSA name that should always exist once it's created.  */
 244   if (var == var_ann (SSA_NAME_VAR (var))->default_def)
 245     return;
 246
 247   /* If the ssa name is marked for rewriting, it may have multiple definitions,
 248      but we may happen to remove just one of them.  So do not remove the
 249      ssa name now.  */
 250   if (marked_for_rewrite_p (var))
 251     return;
 252
 253   /* release_ssa_name can be called multiple times on a single SSA_NAME.
 254      However, it should only end up on our free list one time.   We
 255      keep a status bit in the SSA_NAME node itself to indicate it has
 256      been put on the free list.
 257
 258      Note that once on the freelist you can not reference the SSA_NAME's
 259      defining statement.  */
 260   if (! SSA_NAME_IN_FREE_LIST (var))
 261     {
 262       SSA_NAME_IN_FREE_LIST (var) = 1;
 263       TREE_CHAIN (var) = free_ssanames;
 264       free_ssanames = var;
 265     }
 266 }
 267
 268 /* Creates a duplicate of a ssa name NAME defined in statement STMT.  */
 269
 270 tree
 271 duplicate_ssa_name (tree name, tree stmt)
 272 {
 273   tree new_name = make_ssa_name (SSA_NAME_VAR (name), stmt);
 274   struct ptr_info_def *old_ptr_info = SSA_NAME_PTR_INFO (name);
 275   struct ptr_info_def *new_ptr_info;
 276
 277   if (!old_ptr_info)
 278     return new_name;
 279
 280   new_ptr_info = ggc_alloc (sizeof (struct ptr_info_def));
 281   *new_ptr_info = *old_ptr_info;
 282
 283   if (old_ptr_info->pt_vars)
 284     {
 285       new_ptr_info->pt_vars = BITMAP_GGC_ALLOC ();
 286       bitmap_copy (new_ptr_info->pt_vars, old_ptr_info->pt_vars);
 287     }
 288
 289   SSA_NAME_PTR_INFO (new_name) = new_ptr_info;
 290   return new_name;
 291 }
 292
 293
 294 /* Release all the SSA_NAMEs created by STMT.  */
 295
 296 void
 297 release_defs (tree stmt)
 298 {
 299   tree def;
 300   ssa_op_iter iter;
 301
 302   FOR_EACH_SSA_TREE_OPERAND (def, stmt, iter, SSA_OP_ALL_DEFS)
 303     release_ssa_name (def);
 304 }
 305
 306
 307 /* Replace the symbol associated with SSA_NAME with SYM.  */
 308
 309 void
 310 replace_ssa_name_symbol (tree ssa_name, tree sym)
 311 {
 312   SSA_NAME_VAR (ssa_name) = sym;
 313   TREE_TYPE (ssa_name) = TREE_TYPE (sym);
 314 }
 315
 316 #include "gt-tree-ssanames.h"